Different steel or iron based materials are usually joined by brazing with Ni-, Ag- or Cu-brazing materials.
Brazing is a process for tightening/joining, at which the temperature is lower than the solidus temperature of the base material of the objects which are to be joined together/tightened.
Brazing materials consist of material for joining and tightening, which completely or partly melt during the brazing process.
U.S. Pat. No. 4,135,656 relates to a Ni-based alloy which contains, counted as percentage by weight, 19-23% Mn, 5-8% Si, 4-6% Cu, 0.6-1.8% B and balance with Ni apart from smaller amounts of other elements. U.S. Pat. No. 4,314,661 describes another kind of Ni-based alloy which contains, given as a percentage of atoms 0-4% Fe, 0-21% Cr, 0-19% B, 0-12% Si, 0-22% P and balance with Ni.
When brazing with Cu one generally uses pure or almost pure Cu. The pure copper brazing material has a well defined melting point, while nickel brazing materials depending on the fact that they are alloys often have a melting interval.
When joining plates of stainless steel in plate heat exchanger copper brazing materials are often used. Copper is however not suitable for all kinds of applications. The use of brazing materials of copper for food applications is not allowed, but it is used in plate heat exchangers for district heating and for tap water installations.
Heat exchangers joined with brazing material of nickel are used in man applications and are also allowed for a limited number of food applications.
If brazing materials containing nickel alloys are used for joining objects of iron or non nickel-based materials, the composition of the brazed joints differs significantly from the composition of the materials, which are joined. This can result in undesired differences in the chemical and mechanical properties.